Plant growth-promoting function evaluation testing is a specialized laboratory process that verifies the ability of microbial strains and biological products to enhance plant growth through nitrogen fixation, nutrient solubilization, siderophore secretion, and phytohormone production. This testing provides manufacturers, researchers, and regulatory bodies with objective, science-based evidence of functional performance in biofertilizers, microbial inoculants, and biostimulants. Accredited third-party laboratories conduct these evaluations using standardized culture-based, biochemical, molecular, and plant bioassay methods aligned with recognized ISO, EN, and GB frameworks.
Technical Overview
Growth-promoting function evaluation testing refers to the systematic laboratory assessment of traits that enable beneficial microorganisms—primarily plant growth-promoting rhizobacteria (PGPR) and beneficial fungi such as Bacillus, Pseudomonas, Azotobacter, Rhizobium, and Trichoderma species—to stimulate plant growth and development. These functions operate through two principal mechanisms. Direct promotion includes biological nitrogen fixation, solubilization of phosphorus, potassium, and micronutrients, and biosynthesis of phytohormones such as indole-3-acetic acid (IAA), gibberellins, and cytokinins. Indirect promotion includes suppression of soil-borne pathogens, production of lytic enzymes, and enhancement of plant tolerance to abiotic stress through ACC deaminase activity.
This evaluation is essential for microbial inoculants intended for agricultural use, including products within the scope of GB 20287 for microbial inoculants, as well as for bio-organic fertilizers, biostimulants, and functional fermentation products. A comprehensive assessment typically combines in vitro functional screening, molecular confirmation of functional genes, and in vivo plant trials, providing a complete evidence chain from strain capability to actual growth-promoting efficacy.
Testing Samples
Microbial Inoculants and Biofertilizers
Commercial liquid, powder, and granular inoculant products are tested to verify that the declared functional strains retain their growth-promoting activity after production, formulation, and storage. Testing confirms both viable counts and functional trait expression.
Functional Strain Isolates
Pure cultures isolated during research and development, including rhizosphere bacteria, endophytes, actinomycetes, and beneficial fungi, are screened to characterize their growth-promoting potential and to support strain selection and improvement programs.
Biostimulants and Bio-Organic Products
Products combining microbial agents with organic carriers, fermentation broths, or nutrient substrates are evaluated to substantiate functional claims and to ensure consistency between production batches.
Soil, Rhizosphere, and Compost Samples
Environmental samples are analyzed to assess the functional diversity of native microbial communities, evaluate compost maturity, and monitor soil biological health after application of microbial products.
Testing Items
Testing programs are structured around direct and indirect growth-promoting traits, allowing clients to select individual items or a complete functional profile.
- Biological nitrogen fixation capacity (nitrogenase activity and nifH gene detection)
- Inorganic phosphate solubilization
- Organic phosphate mineralization (phytase activity)
- Potassium solubilization
- Zinc and other micronutrient solubilization
- Siderophore production
- Indole-3-acetic acid (IAA) production
- Gibberellin and cytokinin secretion
- ACC (1-aminocyclopropane-1-carboxylate) deaminase activity
- Ammonia and exopolysaccharide (EPS) production
- Hydrolytic enzyme activities (cellulase, protease, amylase, lipase)
- Chitinase and glucanase activities
- Hydrogen cyanide (HCN) production
- Antagonistic activity against phytopathogens such as Fusarium, Phytophthora, and Ralstonia solanacearum
- Biofilm formation and root colonization capability
Testing Methods
Culture-Based Functional Screening
Selective and differential media are used to detect and semi-quantify functional traits. Pikovskaya medium with insoluble phosphate is used to measure solubilization halos, Aleksandrov medium evaluates potassium release, chrome azurol S (CAS) agar detects siderophore secretion, and dual-culture confrontation plates quantify pathogen inhibition zones.
Biochemical and Chromatographic Quantification
Colorimetric and instrumental methods provide quantitative results, including the Salkowski assay for IAA, the acetylene reduction assay for nitrogenase activity, spectrophotometric enzyme activity assays, and high-performance liquid chromatography (HPLC) for precise phytohormone quantification.
Molecular Biology Analysis
Polymerase chain reaction (PCR) and quantitative PCR (qPCR) confirm the presence and expression of functional genes such as nifH, ipdC, and acdS, while 16S rRNA and ITS sequencing verify strain identity and support intellectual property documentation.
Plant Bioassays and Pot Trials
In vivo verification includes seed germination and root elongation tests, sterile substrate pot experiments, and greenhouse efficacy trials measuring biomass accumulation, root architecture, chlorophyll content, and nutrient uptake, following internationally recognized experimental design principles.
Applications
Growth-promoting function evaluation testing serves multiple stakeholders across the agricultural and biological products value chain:
- Regulatory registration and certification support for biofertilizers and microbial inoculants
- Strain screening, selection, and optimization during research and development
- Quality control and batch release testing for manufacturers
- Substantiation of functional claims for product labeling and marketing
- Scientific support for academic research and publication
- Assessment of soil biological health and compost functional maturity
FAQ
What is growth-promoting function evaluation testing?
It is a laboratory assessment that measures whether a microorganism or biological product possesses traits capable of enhancing plant growth, such as nitrogen fixation, phosphate and potassium solubilization, siderophore and phytohormone production, and pathogen suppression. The evaluation combines in vitro screening, molecular detection, and plant-based verification.
What sample types can be submitted for testing?
Accepted samples include commercial microbial inoculants, pure strain isolates, biostimulants, bio-organic fertilizers, fermentation products, and environmental samples such as soil, rhizosphere material, and compost.
Which methods and standards are applied?
Testing follows recognized culture-based, biochemical, chromatographic, and molecular methods, with reference to applicable GB standards for agricultural microbial inoculants and internationally harmonized microbiological practices published under ISO and EN frameworks.
How long does the evaluation take?
Standard in vitro functional screening typically requires ten to twenty working days, while projects including molecular analysis or greenhouse pot trials may require four to eight weeks depending on the test items selected and plant growth cycles.
What deliverables are provided after testing?
Clients receive a comprehensive test report detailing the methods used, quantitative and qualitative results, photographic documentation of plate assays, interpretation of functional capacity, and, where conducted, plant trial efficacy data suitable for internal review or regulatory submission.